A gunman in the US state of California shot and killed six people, including himself and his wife, in a mass shooting that police say has become the “new normal” across the country.

The unidentified man went with his wife to a trucking company in Bakersfield, California, where he shot and killed a man and then turned his gun on his spouse, killing her, Kern County Sheriff Donny Youngblood told a news conference on Wednesday.

He then chased another man from the trucking company before he shot and killed him in front of a nearby sports store.

The gunman then went to a home where he shot and killed a man and a woman, the sheriff said, Presstv reported.

He killed himself shortly afterwards after being confronted by a sheriff’s deputy, Youngblood said.

“This is the new normal, if you look across this country,” Youngblood said, describing the incident as a mass shooting.

"Obviously, these are not random shootings," he added. “Six people lost their lives in a very short period of time.”

Authorities were working to determine “why this started and why so many players were involved and the connection because obviously these are not random shootings,” Youngblood said.

The United States loses around 33,000 people to gun violence every year. Additionally, more than 100,000 people are shot each year in the country at a total cost of $45 billion, according to a study published in the journal Health Affairs.

Amnesty International said in a scathing report Wednesday that the gun violence situation in the United States has grown into a full blown "human rights crisis" amid inaction from the US government.

The report said “all aspects of American life have been compromised in some way by the unfettered access to guns, with no attempts at meaningful national regulation.”

“The US government is prioritizing gun ownership over basic human rights. While many solutions have been offered, there has been a stunning lack of political will to save lives,” said Margaret Huang, executive director of Amnesty International USA.

"Our government has allowed gun violence to become a human rights crisis," she said.

The issue of gun violence has become all the more polarizing under President Donald Trump, a Republican whose presidential campaign was funded partially by the National Rifle Association (NRA).

Trump has been reluctant to address the growing issue in his speeches and following several high-profile mass shootings in the country.